SMITH: TETRADESMUS, A NEW COENOBIC ALGA 77 
and Malinesco (4) (5), and Grintzesco (6), Scenedesmus acutus 
shows great variation under different cultural conditions. The 
regular arrangement of the cells in a linear series may disappear 
and the cells become isolated or arranged in the branching chain- 
like colonies which Naegeli (11) has described under the name of 
Dactylococcus. Although not at all conclusive, the fact is worthy 
of mention here that these investigators found no variation of 
Scenedesmus acutus which looked at all like Tetradesmus. ' 
The alga in question has been under constant observation 
for over nine months and cultivated in different media, such as 
Knop’s solution in different concentrations, Knop’s solution with 
glucose or cane sugar, Beyerinck’s (2) solution, and Knop’s 
solution with 0.2-2% sodium chlorid. It has been cultivated 
under different conditions of illumination and temperature, and 
under none of these conditions has a colony been found with the 
cellular arrangement characteristic of Scenedesmus acutus. Con- 
versely the evidence is just as strong, for I have had several 
different strains of Scenedesmus acutus under observation for the 
same length of time and under the same differing conditions, and 
in these cultures forms resembling Tetradesmus have never been 
found. If Tetradesmus were a cultural form of Scenedesmus acutus, 
the change from one form to the other should have been observed 
in this extensive series of cultures. 
In the size, shape, and structure of the individual cells the two 
species also show constant differences. The cells of Tetradesmus 
wisconsinensis vary in size from 4—5.8 u in width when the alga 
is grown in 0.1% Knop’s solution; those of Scenedesmus acutus 
under the same conditions are 6.2—4.5u in width. When the alga 
is grown in a 1.0% Knop’s solution, the average diameter of the 
Scenedesmus cell increases to 6-7.8 uw, that of the Tetradesmus cell 
remaining practically unchanged. With the change to the 
stronger solution there is no change in the length of the individual 
cells. This change from the acicular to the ovoid-round shape 
of the cell in Scenedesmus acutus, when the concentration of the 
medium is increased, has been already pointed out by Senn (14). 
On the other hand, Tetradesmus shows no appreciable change in 
the shape of the cells when the concentration of the nutritive solu- 
tion is increased. Beyerinck (1) and Senn (14) have shown that 
